Wheat productivity and soil zinc fractionation in response to foliar and soil applications of zinc oxide nanoparticles under alkaline calcareous conditions

Abstract

Abstract Agronomic bio-fortification of wheat with zinc oxide nano-particles (ZnO-NPs) could serve as a promising strategy to enhance zinc (Zn) bioavailability in soil, thereby improving grain yield and grain Zn content. Field experiments were conducted over two consecutive growing seasons to evaluate the effect of applied Zn on Zn fractions in soil. The study also aimed to optimize Zn application rate and method for optimum wheat productivity. Experimental plan comprised of two foliar spray levels (0.25% and 0.5%), three soil addition levels (control, 10 and 20 kg ha−1), and combination of foliar spray and soil addition, making total nine treatments. Six soil Zn fractions were separated, and ranked in order of residual-Zn (79.9%–85.5%) > carbonate-bound-Zn (7.2%–10.4%) > organic matter-bound-Zn (2.9-4.5%) > iron-manganese-oxide-bound-Zn (2.1%–3.2%) > exchangeable-Zn (2.1%–3.2%) > water-soluble-Zn (0.3%–0.9%) during the both growing seasons. The combined application of foliar spray and soil addition at higher level resulted in highest improvements in chlorophyll content by 156.7% and 119.5%, photosynthetic rate 68.6% and 95.3%, grain yield 29.6% and 32.4%, and grain Zn concentration 105.4% and 121.3% during 2022 and 2023, respectively compared with the control. Grain quality attributes were also maximally enhanced by combined application, with increases in protein content by 41.4% and 38.2%, fat content 77.5% and 63.1%, and fiber content 65.6% and 76.3% during 2022 and 2023, respectively compared with the control. Therefore, combined application of ZnO-NPs via foliar spray and soil addition could be recommended as an effective approach for improving wheat productivity and grain quality under alkaline calcareous conditions.